I would start by looking up the hierarchy of literature to find out where "randomized controlled trials" fit in. The Joanna Briggs Institute has some great resources for ranking studies and figuring out if they are strong or not.

What do you think? Don't just ask us for the answer to your assignment, tell us what you've done to find the answers yourself, then we can help clarify any confusion, and no, asking on AN is not research or studying.